Here are the instructions for it's use since there is no documentation, but Caepolla mentioned that Gaeriel is working on a Window GUI version as well to make things easier.
Just place the 2 .dll files in C:\windows\system directory
Then place the avatar.exe, the 5 blank .tga files along with the picture you want to use as a portrait (in 256x400) in a same directory
Open the MS-DOS window, go the right directory.
The command to type is : avatar.exe filename.ext portraitname sex(f or m)
For instance, to create a portrait from caepolla.jpg named f_caepollaL.tga, you have to type : avatar.exe caepolla.jpg caepolla f
Then, just place the 5 .tga created in your portraits directory. They are ready to use.
We receieved word from Lumina that the source picture can be of any size.